The continuing drive to meet the ever-expanding energy requirements of a burgeoning global population is proving to be one of the biggest challenges facing mankind in the early 21st century. The basic means of energy supply has remained largely unchanged since the dawn of large-scale generation: combustion of fossil fuels such as coal, oil and natural gas still provides the vast majority of electricity, both in the United Kingdom and worldwide. Since the 1960s, however, there has been growing concern about what effect one of the principal products of this combustion, carbon dioxide (CO2), is having on the climate of our world. Climate scientists are now in near-universal agreement that our continued reliance on fossil fuel combustion is increasing the levels of atmospheric CO2 at a rate that will cause a substantial warming of our planet if left unchecked.
Reliance upon fossil fuels for the majority of electricity generation, transport and domestic heating or cooling has pushed the levels of the greenhouse gas carbon dioxide (CO2) ever upward. Climate scientists may be correct when they attribute global warming to the escalating levels of CO2 in the atmosphere. Atmospheric CO2 levels rose from 300 ppm to 370 ppm in the 20th Century. As the fossil fuel burn continues the risk of rising global temperatures leading to a runaway effect is greatly feared.
International agreements to reduce CO2 emissions have stalled against the lack of resolve to institute measures to achieve proposed percentage reductions. Moreover agreements to cut amounts of CO2 which if implemented would still not stop escalating CO2 levels in the atmosphere are not an adequate solution and this only goes to illustrate the scale of the problem. In contrast, universal adoption of the present invention would completely prevent emissions from electricity supply, with the potential for saving of the order of 14 GTonnes per year of CO2 from entering the atmosphere compared to the International Energy Agency's total account of all emissions from primary fuel combustion globally in 2010 of 30.6 GTonnes per year of CO2.
Currently fossil fuel electricity generating stations release the CO2 formed during combustion into the atmosphere, although there are some pilot studies into CO2 extraction and sequestration, such as at Longannet in Fife, UK. Damage to human health and to eco-systems caused by the pollution of the atmosphere resulting from the combustion of fossil fuels is widely acknowledged. Current technology is inadequate to prevent the damage caused by sulphurous, nitrogenous and particulate pollution of the atmosphere.
Immediate and decisive action is now required on an international scale in order to arrest this rise in atmospheric CO2 before global temperatures increase to levels that will cause severe changes to our environment. Consequently, the search for less polluting (‘greener’) methods of energy generation has gathered pace significantly. Research has focused on two key areas:                the capture of the CO2 produced in fossil-fuel combustion, generally for sequestration; and        effective means for harnessing the vast reserves of energy evidently inherent in nature—so-called renewable energy.        
CO2 recovery (‘carbon-capture’) methods are increasingly attracting large-scale investment, with governments encouraging their development by providing financial incentives to oil and gas multinationals. For example “clean coal technology” is based upon CO2 extraction from the flue gasses and then sequestration by insertion into gas or oil well geological structures. However, the separation of CO2 from the flue gases at a conventional hydrocarbon-fired power plant, while practicable, has two main drawbacks. Firstly, it results in a large drop in efficiency (and therefore profitability) of the plant, due to the recovery process. Secondly, and importantly, there are no guarantees that sequestered CO2 will not, over time, escape from its geological prison and make its way into the atmosphere. Improvements to the ease of CO2 recovery are emerging, notably through investigating the potential to combust the hydrocarbon fuel in O2 rather than air—‘oxyfuel combustion,’ as will be elaborated upon later.[1]
It is self-evident that direct electricity generation from renewable energy sources, such as wind, tidal and solar power, amongst others, represent the greenest method of all, since no CO2 is emitted in this way. However, politicians and the energy industry are naturally reluctant to gamble on a large-scale switch-over to renewable energy sources, while the technology to harness these effectively and reliably remains in its infancy. Many of the most promising sources of renewable energy are plagued by unpredictability. For example, wind turbines generate very intermittently and unreliably, their output being dependent on a constantly-changing force, the strength and direction of the wind at any point in time. Nuclear power, the only large-scale alternative to fossil fuel combustion currently in use, represents the other end of the scale: it is very inflexible, generating at a constant output level and thus poorly placed to respond to sudden peaks or dips in electricity demand, which are common. Since electricity must be used as it is produced, both flexibility and reliability are required in an efficient generating system.
Accordingly, much study has been done into the possibility of converting electricity into other forms of energy, for storage and use to meet subsequent demand. One popular area of study is into the manufacture of combustible gases from alternative energy sources. For example, research has been done both in the United States[2] and in Japan[3] into the possibility of producing methane from solar energy, with a pilot plant being established in the latter case to demonstrate its feasibility.
The present invention provides improved methods of capturing and storing electrical energy, optionally from renewable sources, but also from conventional generation technologies. It also provides a fully-integrated approach to energy storage and generation without the emission of CO2 to the atmosphere. The present invention will describe means to produce electricity reliably when required and local to the demand.